Intake air flow rate measuring device

ABSTRACT

The present disclosure provides an intake air flow rate measuring device. The intake air flow rate measuring device includes a flange, a casing, a flow rate sensor, a humidity sensing element, an element terminal, and a humidity terminal. The humidity terminal is spaced away from the element terminal. A portion of the casing between the element terminal and the humidity terminal is defined as a suppressing portion, and a cross-section of the suppressing portion is defined as a suppressing portion cross-section. An end portion of the casing close to the flange is defined as a base portion, and a cross-section of the base portion is defined as a base portion cross-section. The suppressing portion cross-section is set to be smaller than the base portion cross-section.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 15/647,298 filed on Jul. 12, 2017, which is based on JapanesePatent Application No. 2016-142314 filed on Jul. 20, 2016. The contentsof these applications are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates to an intake air flow rate measuringdevice installed in an engine compartment.

BACKGROUND

In order to improve fuel economy or purifying level of exhaust gas,there has been a demand in recent years for measuring a humidity of anintake air that is to be drawn into an engine. Thus, such an intake airflow rate measuring device is equipped with a humidity sensing elementto measure a humidity of an intake air as well as a flow rate (refer to,for example, JP 2010-151795 A).

JP 2010-151795 A discloses an intake air flow rate measuring device thatis inserted into an intake air duct and is equipped with a humiditysensing element.

Typically, a humidity ratio has been used for controlling an engine. Thehumidity sensing element for detecting such a humidity ratio includes,in addition to a humidity detector to detect a relative humidity, atemperature detector to detect a temperature of the humidity sensingelement itself. Then, the humidity sensing element calculates a humidityratio based on the relative humidity detected and the temperature of thehumidity sensing element.

However, as shown in FIG. 19 illustrating curves of a relative humiditywith respect to a temperature, the slope of each of the relativehumidity curves increases as the temperature increases. Therefore, adetection error may increase as the temperature increases.

In the intake air flow rate measuring device disclosed in JP 2010-151795A, heat in an engine compartment transfers to the humidity sensingelement in the intake air duct through, e.g., a flange of the intake airflow rate device. As a result, the temperature of the humidity sensingelement may be increased by the heat.

If the humidity sensing element is heated, the detection error mayincrease as described above, and therefore accuracy of detecting ahumidity may be deteriorated.

With reference to FIG. 19, one example situation where detectionaccuracy is deteriorated due to an increase of the temperature of thehumidity sensing element will be described. In this example, detectionaccuracy of a relative humidity is set to be within ±3% RH, and ahumidity ratio of an intake air is 18.8 g/kg. When the temperature ofthe intake air is 30° C., the detection error range of the humiditysensing element is 18.3-19.7 g/kg. However, when the temperature of thehumidity sensing element increases to 50° C. due to, e.g., heat in theengine compartment, the detection error range of the humidity sensingelement is substantially deteriorated to 16.4-21.3 g/Kg.

In view of the above, it is an objective of the present disclosure toprovide an intake air flow rate measuring device that is configure toavoid deteriorating a detection error of a humidity due to an increasein a temperature of a humidity sensing element due to heat in an enginecompartment.

SUMMARY

An aspect of the present disclosure provides an intake air flow ratemeasuring device that is inserted into an attachment hole of an intakeair duct introducing an intake air into an engine. The intake air flowrate measuring device measures a flow rate of the intake air flowingthrough the intake air duct. The intake air flow rate measuring deviceincludes a flange, a casing, a flow rate sensor, a humidity sensingelement, an element terminal, and a humidity terminal.

The flange is disposed outside of the intake air duct to cover theattachment hole. The casing extends in both the attachment hole and theintake air duct. The flow rate sensor is disposed in the casing tomeasure a flow rate of the intake air flowing through the intake airduct. The humidity sensing element is disposed in the casing to measurea humidity of the intake air flowing through the intake air duct. Theelement terminal is positioned only inside the intake air duct and iselectrically connected to the humidity sensing element. The humidityterminal passes through the flange.

The humidity terminal is positioned spaced away from the elementterminal. The electric connector is disposed between the humidityterminal and the element terminal to electrically connect the humidityterminal to the element terminal. Heat is less likely to transfer theelectric connector as compared to the humidity terminal and the elementterminal. The portion of the casing between the element terminal and thehumidity terminal is defined as a suppressing portion, and across-section of the suppressing portion is defined as a suppressingportion cross-section. And an end portion of the casing close to theflange is defined as a base portion, and a cross-section of the baseportion is defined as a base portion cross-section. The suppressingportion cross-section is set to be smaller than the base portioncross-section.

The suppressing portion cross-section is set to be smaller than the rootportion cross-section. Thus, since heat outside of the intake air ductis restricted at the suppressing portion, heat is suppressed to transferto the humidity sensing element. As a result, it is possible to avoid asituation where a temperature of the humidity sensing element isincreased by heat in the engine compartment, thereby decreasing adetection error of the humidity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a front view of an intake air flow rate measuring deviceviewed from an upstream side of an airflow direction of an intake air;

FIG. 2 is a cross-sectional view of the intake air flow rate measuringdevice taken along the airflow direction of the intake air;

FIG. 3A is a plan view of a humidity sensor;

FIG. 3B is a cross-sectional view of the humidity sensor taken along anelongated direction of the humidity sensor;

FIG. 3C is a cross-sectional view of the humidity sensor taken along adirection perpendicular to the elongated direction;

FIG. 4 is a cross-sectional view of a humidity sensing element;

FIG. 5 is a diagram of a humidity terminal and a flow rate terminal;

FIG. 6A is a diagram describing a root portion cross-section;

FIG. 6B is a diagram describing a suppressing portion cross-section;

FIG. 7 is a diagram of the humidity terminal of the humidity sensor;

FIG. 8 is a cross-sectional view of the humidity sensor taken along theelongated direction;

FIG. 9 is an external view of the humidity sensor;

FIG. 10 is a cross-sectional view of the humidity sensor taken along theelongated direction;

FIG. 11 is a cross-section view of the humidity sensor taken along theelongated direction;

FIG. 12 is a diagram of the suppressing portion;

FIG. 13 is a front view of the intake air flow rate measuring deviceviewed from an upstream side of the airflow direction of the intake air;

FIG. 14 is a front view of the intake air flow rate measuring deviceviewed from an upstream side of the airflow direction of the intake air;

FIG. 15 is a side view of the intake air flow rate measuring device;

FIG. 16 is a cross-sectional view taken along XVI-XVI line in FIG. 15;

FIG. 17 is a diagram of the intake air flow rate measuring devicewithout a right cover;

FIG. 18A is a diagram of the root portion cross-section;

FIG. 18B is a diagram of the suppressing portion cross-section;

FIG. 19 is graphs showing a relationship between a relative humidity, ahumidity, and a humidity ratio (prior art); and

FIG. 20 is a schematic view of a comparative example of an intake airflow rate measuring device.

DETAILED DESCRIPTION

It is needless to say that following embodiments are some examples ofthe present disclosure, and therefore the present disclosure is notlimited to these embodiment. Furthermore, each of the substantially samestructures among the embodiments will be assigned to the respectivecommon referential numeral and the description of the substantially samestructures will be omitted in the subsequent embodiments.

First Embodiment

Referring FIGS. 1 to 7, a first embodiment of the present disclosurewill be described below.

An intake air flow rate measuring device 100 is disposed in an intakeair duct D introducing an intake air to an engine for a vehicle. Thatis, the intake air flow rate measuring device 100 is disposed in anengine compartment.

The intake air duct D is an outlet of an air cleaner or intake pipe. Theintake air duct D defines an attachment hole Da for the intake air flowrate measuring device 100. The attachment hole Da has a cylindricalshape passing through the intake air duct D.

The intake air flow rate measuring device 100 is inserted into theattachment hole Da and measures a flow rate of the intake air flowingthrough the intake air duct D.

The intake air flow rate measuring device 100 includes a flange 3 a,which is disposed in an outer side of the intake air duct D and coversthe attachment hole Da, and a casing 3, which is disposed in the intakeair duct D.

The casing 3 houses a flow rate sensor 4 and a humidity sensing element13. The flow rate sensor 4 measures a flow rate of the intake airflowing through the intake air duct D. The humidity sensing element 13measures a humidity of the intake air flowing through the intake airduct D.

The casing 3 according to the first embodiment includes a base 1disposed inside the attachment hole Da, a main body 2 having the flowrate sensor 4, and a humidity sensor 12 having the humidity sensingelement 13.

The main body 2 and the humidity sensor 12 are separately supported bythe flange 3 a.

The humidity sensor 12 includes a circuit substrate 15 on which thehumidity sensing element 13 is disposed and a molding resin 17 coveringthe humidity sensing element 13 and the circuit substrate 15.

The intake air flow rate measuring device 100 includes an elementterminal and humidity terminals 18. The element terminal is positionedonly inside the intake air duct D and is electrically connected to thehumidity sensing element 13. The humidity terminals 18 pass through theflange 3 a. Each of the humidity terminals 18 electrically connects theouster side of the flange 3 a to the element terminal inside the intakeair duct D.

In the first embodiment, the above-described circuit substrate 15 servesas the element terminal.

The base 1 is adjacent to the flange 3 a and is formed of the same resinmaterial as the flange 3 a. The attachment hole Da is filled with thebase 1, and a packing such as an O-ring is attached to an outercircumferential surface of the base 1. As a result, when the intake airflow rate measuring device 100 is attached to the intake air duct D, aspace between the attachment hole Da and the base 1 is sealed with thepacking.

It should be noted that although FIGS. 6A and 6B show the cross-sectionof the base 1 with a rectangular shape, the base 1 may have across-section with any other shape such as a circle.

The main body 2 defines therein a passage through which a portion of anintake air flows. The main body 2 is formed of the same resin materialas the flange 3 a. One example of the structure of the passage formed inthe main body 2 will be described below, although the passage may have adifferent structure.

A bypass passage 5 and a sub-bypass passage 6 are defined in the mainbody 2. A portion of the intake air flowing through the intake air ductD flows through the bypass and sub-bypass passages 5, 6.

The bypass passage 5 is a passage allowing a portion of the intake airflowing through the intake air duct D to pass through the bypass passage5. The bypass passage 5 extends along a flow direction of the intake airin the intake air duct D. An intake air inlet 5 a of the bypass passage5 is formed upstream of the intake air duct D, whereas an intake airoutlet 5 b of the bypass passage 5 is formed downstream of the intakeair duct D. A squeezed opening is formed at the intake air outlet 5 b torestrict an amount of the intake air passing through the bypass passage5.

The sub-bypass passage 6 includes a sub inlet 6 a and a sub outlet 6 b.A portion of the intake air flowing through the bypass passage 5 flowsinto the sub inlet 6 a. The intake air passing through the sub-bypasspassage 6 returns to the intake air duct D through the sub outlet 6 b.More specifically, the sub-bypass passage 6 causes the intake airflowing in through the sub inlet 6 a to go around in the main body 2 andthen to return into the intake air duct D. Although FIGS. 1 and 2 showthe sub outlet 6 b of the sub-bypass passage 6 formed outside the bypasspassage 5, the sub outlet 6 b may serve to cause the intake air passingthrough the sub-bypass passage 6 to return to the bypass passage 5again.

A connector 7 is disposed in an outside portion of the intake air flowrate measuring device 100 that is positioned outside of the intake airduct D. The connector 7 is electrically connected to an externalequipment such as an engine control unit. The connector 7 is formed ofthe same resin material as the flange 3 a.

The flow rate sensor 4 is a thermal type sensor to measure a flow rateof the intake air flowing through the sub-bypass passage 6 based on athermal detection value. A chip type with a thinner substrate or abobbin type resistance may be used for the flow rate sensor 4.

FIG. 2 shows one example of the flow rate sensor 4 that is a chip typearranged inside the main body 2 in an assembled state.

The flow rate sensor 4 includes a sensor substrate 8 including a flowrate detector 8 a that detects a flow rate of the intake air. The flowrate sensor 4 also includes a flow rate sensor circuit 9 electricallyconnected to the connector 7. The flow rate sensor 4 includes a circuitbody 4 a housing the flow rate sensor circuit 9.

It should be noted that the flow rate sensor circuit 9 is configured tocompensate a flow rate detected by the flow rate detector 8 a using thetemperature of the intake air, and to output a flow rate signal beingconverted into digital form after the compensation.

The main body 2 is formed of the same resin material as the flange 3 a.A plurality of flow rate terminals 10, which are electrically connectedto the flow rate sensor 9, are disposed inside the main body 2 inaddition to the circuit body 4 a (see FIG. 5). An end of each of theflow rate terminals 10 enters into the connector 7. Specifically, theconnector 7 shown in FIG. 1 is a so-called male connector and a femaletype resin coupler, which is made of the same resin material as theflange 3 a, is disposed in the connector 7. Then, the end of each of theflow rate terminals 10 is arranged inside the resin coupler.

The intake air flow rate measuring device 100 includes an intake airtemperature sensor 11 to measure a temperature of the intake air flowingthrough the intake air duct D.

The intake air temperature sensor 11 is disposed outside of the mainbody 2 as shown in FIG. 2 and measures a temperature of the intake airflowing through an area outside of the main body 2. More specifically,the intake air temperature sensor 11 is disposed in a position spacedaway from the main body 2 so as not to be affected by heat from the mainbody 2.

The intake air temperature sensor 11 shown in FIG. 1 is a thermistorusing a bobbin type resistance. The intake air temperature sensor 11includes a thermistor body having variable resistance depending on atemperature and two leads extending from the thermistor body. The twoleads are supported by a protrusion, and therefore the thermistor bodyis supported at the area spaced away from the main body 2 by a certaindistance.

The temperature signal of the intake air measured by the intake airtemperature sensor 11 may be obtained as a voltage of the resistancevariation or output after being converted to digital.

The intake air flow rate measuring device 100 includes the humiditysensor 12 that measures a humidity of the intake air flowing through theintake air duct D. The specific description of the humidity sensor 12will be described with reference to FIGS. 3 to 7. In the followingdescription, an up-and-down direction of the intake air duct D in FIG. 1is defined as an x-axis direction and a right-and-left direction of theintake air duct D in FIG. 2 is defined as a y-axis direction.Furthermore, a direction along which a center axis of the cylindricalshape of the intake air duct D extends, in other words, a flow directionof the intake air flowing through an area outside of the main body 2, isdefined as a z-axis direction.

The humidity sensor 12 has a plate shape. Hereinafter, a direction alongwhich the longest side of the humidity sensor 12 extends, i.e., anup-and-down direction of FIG. 3B, is defined as an x1 direction. Adirection along which the shortest side of the humidity sensor 12extends, i.e., a right-and-left direction in FIG. 3B, is defined as a y1direction. Further, a direction along which the second longest side ofthe humidity sensor 12 extends, i.e., a right-and-left direction in FIG.3C is defined as a z1 direction.

The humidity sensor 12 of the first embodiment is supported by theflange 3 a and the base 1 with being separate with the main body 2, asshown in FIG. 1, and measures a humidity of the intake air flowingthrough an area outside of the main body 2.

The humidity sensor 12 is disposed at a position spaced away from themain body 2 so as not to be affected by heat from the main body 2 whileallowing the intake air passing through the intake air duct D to collidewith the humidity sensor 12 (i.e., the humidity sensor 12 is directlyexposed to the intake air).

The humidity sensor 12 is arranged so that the x1 direction of thehumidity sensor 12 is parallel with the x-direction of the intake airduct D, the y1 direction of the humidity sensor 12 is parallel with they-direction of the intake air duct D, and the z1 direction of thehumidity sensor 12 is parallel with the z-direction of the intake airduct D.

That is, the elongated surface of the humidity sensor 12 extending alongthe z1 direction is arranged to be parallel with the flow direction ofthe intake air.

The structure of the humidity sensor 12 will be described in detailbelow.

The humidity sensor 12 includes the humidity sensing element 13 thatmeasures a humidity of the intake air.

The humidity sensor 12 includes a humidity sensor circuit 14 thatoutputs a humidity signal of the humidity sensing element 13.

The humidity sensing element 13 and the humidity sensor circuit 14 aremounted on the circuit substrate 15.

The humidity sensor 12 includes a heat radiating plate 16 made of ametal.

The heat radiating plate 16 serves to make the temperatures of thehumidity sensing element 13 and the humidity sensor circuit 14 close tothe temperature of the intake air.

The humidity sensor 12 includes the molding resin 17 that covers thehumidity sensing element 13 on the circuit substrate 15 and the humiditysensor circuit 14.

The humidity sensing element 13 is configured to obtain a humidityratio. For example, a commercially available IC for sensing a humiditymay be used as the humidity sensing element 13. More specifically, thehumidity sensing element 13 includes a humidity detector 13 a thatdetects a relative humidity and a temperature detector that detects atemperature of the humidity sensing element 13. Then, the humiditysensing element 13 calculates the humidity ratio from the relativehumidity detected by the humidity detector 13 a and the temperaturedetected by the temperature detector, and outputs the humidity ratio asa humidity signal.

The humidity detector 13 a is a device utilizing a capacitance change.In the humidity detector 13 a, capacitance varies in accordance with arelative humidity of the intake air in contact with the humiditydetector 13 a. For example, the humidity detector 13 a is formed of ahumidity-sensitive material 13 b such as polyimide and two electrodes 13c. More specifically, as shown in FIG. 3B, two electrodes 13 c arearranged on a silicon substrate 13 d serving as a base, and then the twoelectrodes 13 c are disposed inside the humidity-sensitive material 13b.

The humidity-sensitive material 13 b is directly exposed to the intakeair. An amount of water molecules contained in the humidity-sensitivematerial 13 b varies in accordance with a humidity of the intake air incontact with the humidity-sensitive material 13 b. When the amount ofthe water molecules contained in the humidity-sensitive material 13 bvaries, capacitance between the two electrodes 13 c also varies. Themethod to detect the capacitance is similar to a method to detectcapacitance for a small capacitor. For example, the method to detectcapacitance with an LCR that utilizes a change of an oscillationfrequency according to the change in capacitance may be used.

Although the humidity detector 13 a is a device utilizing thecapacitance change as described above in the present embodiment, othertypes of devices such as a device utilizing a resistance change may beused as the humidity detector 13 a.

The humidity sensor circuit 14 is a circuit outputting the humiditysignal generated by the humidity sensing element 13. The humidity sensorcircuit 14 may be formed of a variety of electric components such as anoperational amplifier. The humidity signal from the humidity sensor 12may be an analog signal of a voltage change, or a digital signal.

The circuit substrate 15 is a resin film having a print circuit formedon only a surface on which the humidity sensing element 13 and thehumidity sensor circuit 14 are disposed. The print circuit iselectrically connected to electric components such as the humiditysensing element 13 and the humidity sensor circuit 14.

The circuit substrate 15 has an elongated shape extending along the x1direction. The humidity sensing element 13 is disposed on the circuitsubstrate 15 at a position close to the center of the intake air duct D.The humidity sensor circuit 14 is disposed on the circuit substrate 15at a position closer to the flange 3 a than the humidity sensing element13 is to the flange 3 a.

The heat radiating plate 16 is a radiator made of a metal having highthermal conductivity. The heat radiator 16 is thermally coupled with thehumidity sensing element 13 and the humidity sensor circuit 14. The heatradiating plate 16 is exposed to the intake air flowing through theintake air duct D and serves to make the temperatures of the humiditysensing element 13 and the humidity sensor circuit 14 close to thetemperature of the intake air. The heat radiating plate 16 also servesas a supporting plate that supports the circuit substrate 15.

The molding resin 17 is an insulating resin formed through injectionmolding. More specifically, the molding resin 17 is formed by injectinga molding material to the components forming the humidity sensor 12 thathas been inserted. The molding resin 17 protects the components formingthe humidity sensor 12 and increases rigidity of the humidity sensor 12.

A window portion 17 a is formed by being recessed from the molding resin17. The window portion 17 a guides the intake air directly to thehumidity sensing element 13. In the present embodiment, the windowportion 17 a is arranged to face the main body 2, whereas the heatradiating plate 16 is arranged in an opposite direction from the mainbody 2. However, it may not necessarily limit to this arrangement, andthe opposite arrangement may be used, alternatively.

One end of the molding resin 17 in the elongated direction is insertedinto the flange 3 a and the base 1. Thus, the humidity sensor 12 issupported by both the flange 3 a and the base 1.

The molding resin 17 may have any shape of a cross-section. For example,the molding resin 17 may have a shape having a round shape at a cornerthereof to reduce a resistance against the flow of the intake air.Alternatively, the molding resin 17 may have an upstream end and adownstream end both of which has a streamlined shape or a tapered shapeso as to reduce the intake air flow resistance.

The humidity sensor 12 includes a plurality of humidity terminals 18.Each of the humidity terminals 18 has a portion inside the molding resin17. Each of the humidity terminals 18 is electrically connected to thecircuit substrate 15, and is an elongated metal plate formed by pressinga metal film having conductivity.

The humidity terminals 18 and the circuit substrate 15 are spaced awayfrom each other along the x1 direction. In other words, a physical spacebetween an end of each of the humidity terminals 18 closest to thecircuit substrate 15 and an end of the heat radiating plate 16 closestto the humidity terminal 18 exists.

Electric connectors 19 are disposed between the humidity terminals 18and the circuit substrate 15. The electric connectors 19 electricallyconnect the humidity terminals 18 to the circuit substrate 15. In thefirst embodiment, the electric connector 19 is a conductive wiring suchas wire bonding. It should be noted that the wire bonding is atechnology for electrically connecting a metal wiring such as a gold, acopper, or an aluminum by thermo-compressing bonding or ultra-sonicthermo-compressing bonding.

Heat is less likely to transfer through each of the electric connectors19 as compared to the humidity terminals 18 and the circuit substrate15. More specifically, the electric connector 19 is a wiring for thewire bonding, and therefore the electric connector 19 has asubstantially small cross-section. Thus, the thermal conductivity of theelectric connectors 19 is less than that of the humidity terminals 18and the circuit substrate 15.

As shown in FIGS. 3A and 3B, a portion of each of the humidity terminals18 is exposed to an outside of the molding resin 17 in a state where thehumidity sensor 12 is not disposed inside the base 1 and the flange 3 a.

The portions of the humidity terminals 18 outside of the molding resin17 are disposed inside the base 1 and the flange 3 a through insertmolding. In the first embodiment, an end of each of the humidityterminals 18 is electrically connected to the middle of the flow rateterminal 10, as shown in FIG. 5. Alternatively, the end of each of thehumidity terminals 18 may be disposed inside the connector 7 by settingthe humidity terminals 18 independently.

A portion of the casing 3 between the circuit substrate 15 and thehumidity terminals 18 is defined as a suppressing portion α. That is, aportion of the molding resin 17 is the suppressing portion α among thecasing 3.

The cross-section of the suppressing portion α is defined as asuppressing portion cross-section α1. In other words, the cross-sectionof the molding resin 17 among the suppressing portion α is thesuppressing portion cross-section α1. The suppressing portioncross-section α1 is a cross-section formed by cutting the suppressingportion α along a direction perpendicular to the z1 direction. Theportion of the narrowed cross-section α1 is indicated by the broken linein FIG. 1. Further, FIG. 6B shows the cross-sections of the main body 2and the humidity sensor 12 formed by cutting the suppressing portion αin a direction perpendicular to the x1 direction.

The end of the casing 3 close to the flange 3 a is defined as a baseportion 3. The base portion β is the end of the base 1 close to theflange 3 a.

The cross-section of the base portion β is defined as a base portioncross-section β1. That is, the cross-section of the base 1 formed of aresin is defined as the base portion cross-section β1. The base portioncross-section β1 is a cross-section cutting the base β in a directionperpendicular to the x-axis direction, and the portion of the baseportion cross-section β1 is indicated by the broken line in FIG. 1.Further, FIG. 6A shows a cross-section formed by cutting the base β in adirection perpendicular to the x-axis direction.

For a comparative reason, FIG. 20 shows a comparative example of anintake air flow rate measuring device 100 in which the correspondingpositions of the suppressing portion cross-section α1 and the baseportion cross-section β1 are indicated. As shown in FIG. 20, thesuppressing portion cross-section α1 and the base portion cross-sectionβ1 are the same.

In the intake air flow rate device 100 according to the presentembodiment, the suppressing portion cross-section α1 is formed to besmaller than the base portion cross-section β1.

By making the suppressing portion cross-section α1 smaller than the baseportion cross-section β1, the thermal resistance of the suppressingportion α can be increased. As a result, even when heat outside of theintake air duct D is transferred to the humidity sensor 12 through theflange 3 a, transfer of the heat to the humidity sensing element 13 isrestricted by the suppressing portion α. Hereinafter, this effect by thesuppressing portion α is referred to as a “first effect”.

Further, by making the suppressing portion cross-section α1 smaller thanthe base portion cross-section β1, heat capacity of the suppressingportion α can be reduced. Thus, the suppressing portion α can be easilycooled. As a result, the temperature of the suppressing portion α can beeasily decreased by the intake air flowing through the intake air ductD. Hereinafter, this effect of the suppressing portion α is referred toas a “second effect”.

According to the first and second effects, heat transfer through thesuppressing portion α can be suppressed. Thus, even when heat outside ofthe intake air duct D is transferred to the humidity sensor 12 throughthe flange 3 a, heat transfer to the humidity sensing element 13 can berestricted by the suppressing portion α.

Accordingly, an increase in the temperature of the humidity sensingelement 13 due to, e.g., heat in the engine compartment can be avoided.Thus, the temperature of the humidity sensing element 13 can besubstantially the same as the temperature of the intake air flowingthrough the intake air duct D. As a result, a detection error of thehumidity due to the heat in the engine compartment can be suppressed. Inother words, the humidity (more specifically, the humidity ratio) of theintake air flowing into the engine can be accurately detected by thehumidity sensor 12 disposed in the intake air flow rate measuring device100.

In the first embodiment, the main body 2 and the humidity sensor 12 areseparately (independently) supported by the flange 3 a and the base 1.Heat transfer from an outside of the intake air duct D is divided intothe main body 2 and the humidity sensor 12. Thus, a heat amounttransferred to the humidity sensor 12 can be reduced. The heattransferred to the humidity sensor 12 is further released by the intakeair flowing through the intake air duct D.

In this way, the first embodiment has a structure that suppresses heatoutside of the intake air duct D to transfer to the humidity sensor 12.In addition, the suppressing portion cross-section α1 is smaller thanthe base portion cross-section β1. Thus, heat transfer to the humiditysensor 13 over the suppressing portion cross-section α1 and the electricconnectors 19 can be further reduced.

The thermal resistance of the electric connectors 19 is greater thanthat of the humidity terminals 18.

Therefore, the heat transfer suppressing effect by the electricconnectors 19 can be enhanced, and thus heat transfer to the humiditysensor 13 through the electric connectors 19 can be suppressed. As aresult, it is possible to avoid a situation where the humidity sensor 13is heated by heat transferred from the outside through the humidityterminals 18.

Each of the electric connectors 19 according to the first embodiment isa metal wiring, such as a gold, a copper, or an aluminum, subject towire bonding.

By using such an electric connector, the cross-section of thereof forelectric connection can be small. Thus, thermal resistance of theelectric connectors 19 can be increased, and therefore the heat transfersuppressing effect by the electric connectors 19 can be increased.Further, by using the wire bonding technology, productivity duringelectric connection between the humidity terminals 18 and the circuitsubstrate 15 can be increased.

That is, by using the wirings subject to the wire bonding as theelectric connectors 19, the heat transfer suppressing effect by theelectric connectors 19 and the productivity of the electric connectionprocess can be improved at the same time.

The thermal conductivity of each of the humidity terminals 18 is lessthan the flow rate terminal 10. For example, the flow rate terminals 10are formed of a copper. In contrast, the humidity terminals 18 areformed of phosphor bronze having thermal conductivity less than thecopper.

In this way, by forming the humidity terminals 18 with metallic materialhaving low thermal conductivity, an amount of heat transferred to theelectric connectors 19 through the humidity terminals 18 can be reduced,and as a result heat reaching the humidity sensing element 13 can bereduced.

Each of the humidity terminals 18 has a shape tapered toward the circuitsubstrate 15 as shown in FIG. 7.

In FIG. 7, the width of the furthest portion of each of the humidityterminals 18 away from the circuit substrate 15 is represented as d1whereas the width of the closest portion of each of the humidityterminals 18 to the circuit substrate 15 is represented as d2. Then, thewidth d1 and the width d2 can be represented as d1>d2.

The thickness of the furthest portion and the thickness of the closestportion are the same. Thus, the cross-section of each of the humidityterminals 18 at a position close to the circuit substrate 15 is smallerthan the cross-section of each of the humidity terminals 18 at aposition away from the circuit substrate 15. As a result, thermalresistance of each of the humidity terminals 18 at a position close tothe circuit substrate 15 is greater than thermal resistance of each ofthe humidity terminals 18 at a position away from the circuit substrate15.

In this way, since each of the humidity terminals 18 has a shape taperedtoward the circuit substrate 15, the thermal conductivity of thehumidity terminals 18 gradually increases according to the positions ofthe humidity terminals 18 toward the electric connectors 19. Therefore,heat transfer toward the electric connectors 19 through the humidityterminals 18 can be reduced, and as a result an amount of heat reachingthe humidity sensing element 13 can be decreased.

In the first embodiment, the suppressing portion α is positioned, in astate where the intake air flow rate measuring device 100 is attached tothe intake air duct D, such that the suppressing portion α is exposed tothe intake air flowing through the intake air duct D. Specifically, whenviewed from an upstream side of the intake air duct D, the suppressingportion α is positioned inside the intake air duct D.

Therefore, the suppressing portion α can be forcibly cooled by theintake air flowing through the intake air duct D. Thus, heat from theoutside of the intake air duct D can be suppressed to transfer to thehumidity sensing element 13 through the suppressing portion α.

Modification to First Embodiment

In the above-described embodiment, to reduce intake air resistance, thehumidity sensor 12 is arranged such that the elongated surface of thehumidity sensor 12 along the z1 direction is parallel with the flowdirection of the intake air. Alternatively, the elongated surface of thehumidity sensor 12 along the z1 direction may be angled with the flowdirection of the intake air. Accordingly, the suppressing portion α canmore actively receive the intake air, and thus the effect of cooling thesuppressing portion α can be enhanced.

As another embodiment, a plurality of recessed portions may be formed ona surface of the suppressing portion α to increase a heat exchangeefficiency between the suppressing portion α and the intake air.Accordingly, cooling effects on the suppressing portion α can beincreased, and as a result the heat transfer suppressing effect by thesuppressing portion α can be improved.

Second Embodiment

Next, the second embodiment will be described with reference to FIG. 8.

In the second embodiment, a recessed portion γ are formed in the moldingresin 17 to further decrease the suppressing portion cross-section α1.

The recessed portion γ makes the thickness of the suppressing portion αalong the y1 direction thinner than the thickness of other portions ofthe molding resin 17 along the y1 direction, as shown in FIG. 8.

Accordingly, the suppressing portion cross-section α1 can be made muchsmaller, and therefore thermal resistance of the suppressing portion αcan be further increased. Furthermore, it is possible to furtherdecrease heat capacity of the suppressing portion α, and thus thesuppressing portion α can be easily cooled. As a result, the heattransfer suppressing effect by the suppressing portion α can beimproved.

Third Embodiment

Next, the third embodiment will be described with reference to FIG. 9.

In the third embodiment, two recessed portions γ are formed in themolding resin 17 to further decrease the suppressing portioncross-section α1, as with the second embodiment.

The two recessed portions γ make the thickness of the suppressingportion α along the z1 direction thinner than the thickness of otherportions of the molding resin 17 along the z1 direction, as shown inFIG. 9.

Accordingly, the same advantages as the second embodiment can beobtained.

Fourth Embodiment

Next, the fourth embodiment will be described with reference to FIG. 10.

In the fourth embodiment, a ceramic substrate is used as the electricconnector 19. The ceramic substrate is made by printing a conductivemetallic pattern on a surface of a ceramic having thermal conductivitylower than the molding resin 17. The metallic pattern may be formed of acopper or silver.

By using the ceramic substrate as the electric connector 19, thermalresistance of the electric connector 19 can be increased. Therefore, theheat transfer suppressing effect by the suppressing portion α can beimproved. Further, by using the ceramic substrate, productivity duringelectric connection between the humidity terminals 18 and the circuitsubstrate 15 can be increased. Furthermore, strength of the suppressingportion α can be improved by using the ceramic substrate.

That is, the heat transfer suppressing effect by the electric connector19, productivity for electric connecting process, and strength of thesuppressing portion α can be improved at the same time by using theceramic substrate as the electric connector 19.

Fifth Embodiment

Next, the fifth embodiment will be described with reference to FIG. 11.

In the fifth embodiment, a flexible substrate is used as the electricconnector 19. The flexible substrate is made by printing a conductivemetallic pattern on a surface of a resin insulating film. The metallicpattern may be formed of a copper or silver.

By using the flexible substrate as the electric connector 19, thermalresistance of the electric connector 19 can be increased. Therefore, theheat transfer suppressing effect by the electric connector 19 can beimproved. Further, by using the flexible substrate, productivity duringelectric connection between the humidity terminals 18 and the circuitsubstrate 15 can be increased.

That is, the heat transfer suppressing effect by the electric connector19 and productivity for electric connecting process can be improved atthe same time by using the flexible substrate as the electric connector19.

Sixth Embodiment

Next, the sixth embodiment will be described with reference to FIG. 12.

In the sixth embodiment, an opening δ is formed in the molding resin 17such that the electric connectors 19 are directly exposed to the intakeair flowing through the intake air duct D.

FIG. 12 shows the opening δ that passes through the molding resin 17 inthe thickness direction thereof. Alternatively, the opening δ may berecessed from the molding resin 17 such that the electrical connectors19 are directly exposed to the intake air.

By providing the opening δ, the electric connectors 19 can be directlycooled by the intake air. Thus, the heat transfer suppressing effect bythe electric connectors 19 can be improved.

It should be noted that the opening δ may be applied to the seventhembodiment as described below.

Seventh Embodiment

Next, the seventh embodiment will be described with reference to FIG.13.

In the seventh embodiment (and the eighth embodiment described later),the humidity sensing element 13 and the suppressing portion α aredisposed in the main body 2.

The casing 3 includes the main body 2 having both the flow rate sensor 8and the humidity sensing element 13. Then, a portion of the main body 2in the casing 3 serves as the suppressing portion α.

More specifically, in the seventh embodiment, the circuit substrate 15is disposed inside the main body 2. The humidity sensing element 13 ispositioned to be exposed to the intake air inside the bypass passage 5or the sub-bypass passage 6 to detect a humidity of the intake air. Itshould be noted that the location of the humidity sensing element 13 isnot necessarily limited to the above. For example, the humidity sensingelement 13 may be positioned outside the main body 2 to detect ahumidity of the intake air flowing through an outside are of the mainbody 2.

As with the first embodiment, the humidity terminals 18 and the circuitsubstrate 15 are spaced away along the x-axis direction from each other.The humidity terminals 18 and the circuit substrate 15 are electricallyconnected to each other through the electric connectors 19.

Although the circuit substrate 15 is disposed inside the main body 2,the humidity terminals 18 and the circuit substrate 15 are spaced awayfrom each other, as described above. Then, the portion of the main bodywhere the humidity terminals 18 and the circuit substrate 15 are spacedaway from each other serves as the suppressing portion α.

In the seventh embodiment, the suppressing portion α is formed in themain body 2, the base portion β is formed in the base 1. The main body 2has a cross-section smaller than the base 1. Thus, the suppressingportion cross-section α1 can be smaller than the base portioncross-section 131.

Even when the humidity sensing element 13 is disposed in the main body 2as described above, heat transfer from an outside of the intake air ductD to the humidity sensing element 13 can be suppressed by thesuppressing portion cross-section α1 that is smaller than the baseportion cross-section 131.

Furthermore, in the seventh embodiment, the recessed portion γ is formedat the suppressing portion α to further narrow the suppressing portioncross-section α1. Accordingly, thermal resistance of the suppressingportion α can be increased, thereby suppressing heat from an outside ofthe intake air duct D to transfer to the humidity sensing element 13.Instead of the recessed portion γ, the suppressing portion cross-sectionα1 may be narrowed by forming a space inside the suppressing portion α(see the housing space 40 in the eighth embodiment described later).

In addition to the above-described structures, a measuring space (seethe humidity sensing space 21 b in the eighth embodiment describedlater) through which the intake air flows may be formed in the centerregion of the intake air duct D. The humidity sensing element 13 may bearranged inside the measuring space. According to this arrangement, thehumidity sensing element 13 is spaced away from the wall of the intakeair duct D as much as possible, and is surrounded by the main body 2.Thus, it is possible to prevent radiant heat released from the wall ofthe intake air duct D as far-infrared radiation from reaching thehumidity sensing element 13.

As a result, heat transfer from the outside can be suppressed by thesuppressing portion α, and therefore an increase in the temperature ofthe humidity sensing element 13 can be suppressed. Furthermore, theradiant heat from the wall can be blocked by the member surrounding thehumidity sensing element 13, thereby suppressing an increase in thetemperature of the humidity sensing element 13.

Eighth Embodiment

Next, the eighth embodiment will be described with reference to FIGS. 14to 17.

The flow rate sensor 4 is formed as a sensor module integrally havingthe flow rate detector 8 a and the humidity sensing element 13. That is,the casing 3 includes the main body 2 integrally having the flow ratesensor 8 and the humidity sensing element 13, as with the seventhembodiment. Then, a portion of the main body 2 in the casing 3 serves asthe suppressing portion α.

A plurality of sensor terminals 20 are disposed in the flow rate sensor4 to output/input a signal to/from the flow rate sensor circuit 9. Thesensor terminals 20 are electrically connected to the flow rateterminals 10 and the humidity terminals 18 through the electricconnectors 19.

The sensor terminals 20 electrically connected to the humidity sensingelement 13 correspond to the element terminals.

The flow rate detector 8 a and the humidity sensing element 13 areelectrically connected to the flow rate sensor circuit 9 through wiring(not shown) such as a metal wiring. The flow rate sensor circuit 9 isdisposed between the flow rate detector 8 a and the humidity sensingelement 13. It should be noted that the positions of the humiditysensing element 13 and the flow rate sensor circuit 9 may be reversed sothat the flow rate sensor circuit 9 is positioned between the sensorterminals 20 and the humidity sensing element 13.

The flow rate detector 8 a measures a flow rate of the intake airthrough heat transfer from the intake air flowing through the sub-bypasspassage 6. More specifically, the flow rate detector 8 a includes, as atemperature sensing element, a diaphragm on a flat substrate made of ahigh thermal conductive material such as a silicon or a ceramic. A heatelement to heat the intake air is disposed in the diaphragm, and athermosensitive resistor to detect a temperature of the intake airheated by the heat element is also disposed in the diaphragm. The flowrate sensor circuit 9 controls the heat element by applying an electriccurrent to the heat element and then measures a flow rate of the intakeair based on an amount of heat of the intake air heated by the heatelement. That is, the flow rate sensor circuit 9 processes a signal thatis output from the flow rate detector based on the amount of heat.

The humidity sensing element 13 has a similar structure to the firstembodiment. That is, the humidity sensing element 13 is a deviceutilizing a capacitance change.

The flow sensor circuit 9 is electrically connected to the sensorterminal 20. The flow rate sensor circuit 9 outputs the flow rate to anexternal component outside of the intake air flow rate device 100through the sensor terminal 20.

The flow rate detector 8 a, the humidity sensing element 13, and theflow rate sensor circuit 9 are integrally disposed inside a polymericresin such as a thermosetting resin to form the flow rate sensor 4.

Referring to FIG. 16, the main body 2 of the eighth embodiment will bedescribed below. The main body 2 includes a case 30 a housing the flowrate sensor 4. The main body 2 includes a right cover 30 b attached tothe right surface of the main body 2 and a left cover 30 c attached tothe left surface of the main body 2.

In the eighth embodiment, the flow rate sensor 4 is fixed inside themain body 2 by attaching the right cover 30 b and the left cover 30 c tothe both side surfaces of the case 30 a.

A humidity measuring passage 21 is defined in the main body 2 inaddition to the sub-bypass passage 6. A second intake air inlet 21 a todraw the intake air in is formed in the humidity measuring passage 21 atan upstream side of the case 30 a. The second intake air inlet 21 a isin fluid communication with a humidity sensing space 21 a formed in thecase 30 a. A portion of the case 30 a remains at a position downstreamof the humidity sensing space 21 b. The humidity sensing element 13exists in the humidity sensing space 21 b. A second sub-outlet 21 c influid communication with the humidity sensing space 21 b is open at theright cover 30 b as shown in FIG. 15.

Accordingly, a portion of the intake air flowing through the intake airduct D is taken in through the second intake air inlet 21 a. Then, theportion of the intake air flows through the humidity sensing space 21 band returns into the intake air duct D through the second sub-outlet 21c. The humidity sensing element 13 detects a humidity of the intake airflowing through the humidity sensing space 21 b.

In the bypass passage 5, the intake air inlet 5 a is formed in a frontsurface of the case 30 a facing the upstream side of the intake air ductD, and the intake air outlet 5 b is formed in a back surface of the case30 a facing the downstream side of the intake air duct D. A portion ofthe intake air taken in through the intake air inlet 5 a returns intothe intake air duct D through the intake air outlet 5 b, and theremaining portion flows into the sub-bypass passage 6. The intake air inthe sub-bypass passage 6 passes through the flow rate detector 8 a inthe sub-bypass passage 6, and then returns into the intake air duct Dthrough the sub outlets 6 b formed in the right cover 30 b and the leftcover 30 c.

The humidity sensing space 21 b is formed by recessing the case 30 a.The humidity measuring passage 21 is defined by covering the sidesurfaces of the case 30 a with the right cover 30 b and the left cover30 c.

As shown in FIG. 14, the second intake air inlet 21 a is formed on thefront surface of the case 30 a.

In the eighth embodiment, the second sub-outlet 21 c is formed in theright cover 30 b as shown in FIG. 15.

The flow rate sensor circuit 9 is a large scale integrated circuit(i.e., LSI). Such an LSI has increased its integration in recent years.The flow rate sensor circuit 9 is also electrically connected to pluraldetectors (such as the flow rate detector 8 a and the humidity sensingelement 13). Therefore, the flow rate sensor circuit 9 easily generatesheat. Since the flow rate detector 8 a is affected by heat from otherthan the intake air (e.g., the flow rate sensor circuit 9), accuracy ofmeasuring the flow rate would be deteriorated due to heat other than theintake air.

Then, in the eighth embodiment, the flow rate sensor circuit 9 isindirectly cooled by allowing a portion of the intake air to flowthrough the humidity sensing space 21. That is, heat of the flow ratesensor circuit 9 is less likely effect the flow rate detector 8 a.

As described above, the sensor terminals 20 are connected to thehumidity terminals 18 and the flow rate terminals 10 via the electricconnectors 19. Each of the sensor terminals 20 protrudes from one endsurface of the flow rate sensor 4 opposite to the side in which the flowrate detector 8 a is disposed. The humidity terminals 18 and the flowrate terminals 10 protrude toward the sensor terminal 20.

An end of each of the sensor terminals 20, an end of each of thehumidity terminals 18, an end of each of the flow rate terminals 10, andthe electric connector 19 are positioned inside a housing space 40defined in the case 30 a.

The housing space 40 is a space inside the main body 2 and is separatedfrom the intake air flowing through the intake air duct D.

Specifically, the housing space 40 passes through the case 30 a in adirection along which the right cover 30 b and the left cover 30 c arearranged. The housing space 40 is separated from an outside when theright cover 30 b and the left cover 30 c are attached to the case 30 a.

As with the seventh embodiment, the suppressing portion α is disposed inthe main body 2, and the base portion β is disposed in the base 1. Thecross-section of the main body 2 is smaller than the base 1, andtherefore the suppressing portion cross-section α1 can be smaller thanthe base portion cross-section β1.

As a result, even the humidity sensing element 13 is disposed in themain body 2, heat from an outside of the intake air duct D is lesslikely to transfer to the humidity sensing element 13.

In the eighth embodiment, the housing space 40 is formed in thesuppressing portion α to further reduce the suppressing portioncross-section α1. FIG. 18B shows a cross-section of the suppressingportion α in the main body 2. It should be noted that the cross-sectionof the base portion β is the cross-section of the base 1, as with thefirst embodiment (see FIG. 18A).

In this way, the suppressing portion cross-section α1 is further madesmall by forming the housing space 40 in the suppressing portion α. As aresult, thermal resistance of the suppressing portion α can beincreased. Thus, heat from an outside of the intake air duct D is lesslikely to transfer to the humidity sensing element 13.

In the case 30 a, separations 26 to separate the flow rate detector 8 afrom the humidity sensing element 13 are provided. The flow rate sensor4 is fixed to the case 30 a by the separators 26.

Portions of the separators 26 are involved to define the sub-bypasspassage 6, the humidity measuring passage 21, and the housing space 40.In this way, these passages and the housing space 40 are defined by theseparators 26. Thus, the structure of the intake air flow rate measuringdevice 100 can be simple.

The position of the inlet to take in the intake air and the number ofthe inlet are not necessarily limited to the above as long as the intakeair flowing through the intake air duct D can be taken in through theinlet to flow toward the bypass passage 5 and the humidity measuringpassage 21. In the eighth embodiment, the intake air inlet 5 a and thesecond intake air inlet 21 a are formed in the front surface of theintake air flow rate measuring device 100 that faces the upstream sideof the intake air duct D. Accordingly, the intake air flowing throughthe intake air duct D can be smoothly directed to the bypass passage 5and the humidity measuring passage 21.

In the eighth embodiment, the housing space 40 and the humiditymeasuring passage 21 are formed between the flow rate detector 8 a andthe flange 3 a. Thus, heat transfer from the intake air duct D to theflow rate detector 8 a through the case 30 a can be suppressed.

Further, the position and the number of the outlet to discharge theintake air in the humidity measuring passage 21, i.e., the secondsub-outlet 21 c of the humidity measuring passage 21, are notnecessarily limited to the above as long as a portion of the intake airflowing through the intake air duct D can be guided to the humiditymeasuring passage 21 and returned into the intake air duct D again. Inthe eighth embodiment, the second intake air inlet 21 a is positionedupstream of the second sub-outlet 21 c, and thus it is possible tosuppress the intake air to stay in the humidity measuring passage 21.

In the eighth embodiment, the second sub-outlet 21 c is formed in theright cover 30 b. Thus, strength of the case 30 can be obtained.Further, the humidity sensing element 13 is not less likely to beaffected by a reverse flow of the intake air in the intake air duct D.

It should be noted that the second sub-outlet 21 c may be formed in theleft cover 30 c, or each of the left cover 30 c and the right cover 30 bmay have the second sub-outlet 21 c.

As shown in FIGS. 14 and 15, the opening area of the second sub-outlet21 c is smaller than the second intake air inlet 21 a. Alternatively,the opening area of the second sub-outlet 21 c may be larger than thesecond intake air inlet 21 a. Further, the opening area of the secondsub-outlet 21 c may be the same as the second intake air inlet 21 a.

In the eighth embodiment, the housing space 40 is a space containingair. However, the housing space 40 may be vacuum or filled with a fillersuch as gel or epoxy resin.

In the following description, one surface of each of the sensorterminals 20 on which the sensor terminal 20 is in contact with theelectric connector 19 is defined as a surface A1, and the other surfaceof the sensor terminal 20 opposite to the surface A1 is defined as asurface A2 (see FIG. 16).

One surface on which the flow rate terminal 10 and the humidity terminal18 are in contact with the electric connector 19 is defined as a surfaceB1, and the other surface opposite to the surface B1 is defined as asurface B2.

As shown in FIG. 16, the right cover 30 b includes a first protrusion 30d protruding toward the surface A2 of the sensor terminal 20. The firstprotrusion 30 d supports the surface A2 of the sensor terminal 20.

Similarly, the right cover 30 b includes a second protrusion 30 eprotruding toward the flow rate terminal 10 and the humidity terminal18. The surface B2 of the flow rate terminal 10 and the humidityterminal 18 are supported by the second protrusion 30 e.

In this way, due to the existence of the protrusions to support theterminal, wire bonding process to connect each terminal to the electricconnector 19 can be stably performed. In this case, the wire boding isperformed in a state where the right cover 30 b is fixed to the case 30a whereas the left cover 30 c is not connected to the case 30 a.Alternatively, the first protrusion 30 d and the second protrusion 30 emay be disposed in the left cover 30 c, and then the wire bonding may beperformed in a state where the left cover 30 c is fixed to the case 30 awhereas the right cover 30 b is not fixed to the case 30 a.

A squeezed portion 30 f protruding toward the humidity sensing element13 may be formed in either the right cover 30 b or the left cover 30 cto narrow a space of the humidity measuring passage 21.

Furthermore, the intake air temperature sensor 11 may be arranged in thesecond intake air inlet 21 a. Alternatively, the intake air temperaturesensor 11 may be arranged between the second intake air inlet 21 a andthe intake air duct D. Furthermore, the humidity sensing space 21 b maybe formed at a position downstream of the intake air temperature sensor11.

The humidity terminals 18 and the flow rate terminals 10 may be disposedinside the connector 7. Alternatively, to downsize the connector 7, thehumidity detection value and the flow rate detection value may be outputthrough a single terminal to an outside of the intake air flow ratemeasuring device 100.

What is claimed is:
 1. An intake air flow rate measuring device that isinserted into an attachment hole of an intake air duct introducing anintake air into an engine, the intake air flow rate measuring devicemeasuring a flow rate of the intake air flowing through the intake airduct, the intake air flow rate measuring device comprising: a flangethat is disposed outside of the intake air duct to cover the attachmenthole; a casing that extends in both the attachment hole and the intakeair duct; a flow rate sensor that is disposed in the casing to measure aflow rate of the intake air flowing through the intake air duct; ahumidity sensing element that is disposed in the casing to measure ahumidity of the intake air flowing through the intake air duct; anelement terminal that is positioned only inside the intake air duct andis electrically connected to the humidity sensing element; and ahumidity terminal that passes through the flange, wherein the humidityterminal is positioned spaced away from the element terminal, anelectric connector is disposed between the humidity terminal and theelement terminal to electrically connect the humidity terminal to theelement terminal, heat is less likely to transfer through the electricconnector as compared to the humidity terminal and the element terminal,a portion of the casing between the element terminal and the humidityterminal is defined as a suppressing portion, and a cross-section of thesuppressing portion is defined as a suppressing portion cross-section,and an end portion of the casing close to the flange is defined as abase portion, and a cross-section of the base portion is defined as abase portion cross-section, wherein the suppressing portioncross-section is set to be smaller than the base portion cross-section.2. The intake air flow rate measuring device according to claim 1,wherein the casing includes a main body housing the flow rate sensor,and a humidity sensor including the humidity sensing element, the mainbody and the humidity sensor are separately supported by the flange, thehumidity sensor includes a circuit substrate, as the element terminal,on which the humidity sensing element is disposed, and a molding resinthat covers the humidity sensing element and the circuit substrate, andthe suppressing portion is a portion of the molding resin between thecircuit substrate and the humidity terminal.
 3. The intake air flow ratemeasuring device according to claim 1, wherein the casing includes amain body housing both the flow rate sensor and the humidity sensingelement, and the suppressing portion is a portion of the main body ofthe casing.
 4. The intake air flow rate measuring device according toclaim 1, wherein the electric connector has thermal resistance greaterthan that of the humidity terminal.
 5. The intake air flow ratemeasuring device according to claim 4, wherein the electric connector isformed of an electrically conductive wiring subject to wire bonding. 6.The intake air flow rate measuring device according to claim 4, whereinthe electric connector is a ceramic substrate on which a conductivemetallic pattern is printed.
 7. The intake air flow rate measuringdevice according to claim 4, wherein the electric connector is aflexible substrate on which a conductive metallic pattern is printed. 8.The intake air flow rate measuring device according to claim 1, whereinthe casing includes a flow rate terminal that is disposed, separatelywith the humidity terminal, inside the casing and is electricallyconnected to the flow sensor, and the humidity terminal has thermalconductivity less than that of the flow rate terminal.
 9. The intake airflow rate measuring device according to claim 1, wherein the humidityterminal has a shape that is tapered toward the element terminal. 10.The intake air flow rate measuring device according to claim 1, whereinthe suppressing portion is located to be directly exposed to the intakeair flowing through the intake air duct.
 11. The intake air flow ratemeasuring device according to claim 1, wherein the electric connector isdisposed in a housing space defined in the casing.